Clutch mechanism for rotary power tool

ABSTRACT

A clutch mechanism, for use in a rotary power tool having a motor, comprises an input member to which torque from the motor is transferred and an output member co-rotatable with the input member, the output member defining a rotational axis. The clutch mechanism further comprises a cam surface formed on one of the input member or the output member and a compression spring carried by the other of the input member or the output member for co-rotation therewith. The clutch mechanism also comprises a follower having a circular cross-sectional shape biased against the cam surface by the compression spring. In response to relative rotation between the input member and the output member, the cam surface displaces the follower along a line of action coaxial or parallel with the spring. The line of action does not intersect the rotational axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/417,850 filed on Nov. 4, 2016, the entire content of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to rotary power tools, and moreparticularly to clutch mechanisms for rotary power tools.

BACKGROUND OF THE INVENTION

Clutch mechanisms in rotary power tools translate rotary motion of amotor into rotary motion of an output shaft of the tool. Such clutchmechanisms either slip at a fixed predetermined setting or an adjustablesetting to limit the amount of torque from the motor that is transmittedto the output shaft.

SUMMARY OF THE INVENTION

The present invention provides, in one aspect, a clutch mechanism foruse in a rotary power tool having a motor comprises an input member towhich torque from the motor is transferred and an output memberco-rotatable with the input member, the output member defining arotational axis. The clutch mechanism further comprises a cam surfaceformed on one of the input member or the output member and a compressionspring carried by the other of the input member or the output member forco-rotation therewith. The clutch mechanism also comprises a followerhaving a circular cross-sectional shape biased against the cam surfaceby the compression spring. In response to relative rotation between theinput member and the output member, the cam surface displaces thefollower along a line of action coaxial or parallel with the spring. Theline of action does not intersect the rotational axis.

The present invention provides, in another aspect, a clutch mechanismfor use in a rotary power tool having a motor comprises an input memberto which torque from the motor is transferred, the input member havingan interior surface and defining a cam surface recessed in the interiorsurface. The clutch mechanism further comprises an output memberco-rotatable with the input member, the output member carrying acompression spring for co-rotation therewith and defining a rotationalaxis. The clutch mechanism further comprises a follower biased againstthe cam surface by the compression spring. When the motor transferstorque to the input member and the follower is maintained against thecam surface, the output member co-rotates with the input member. Whenthe motor transfers torque to the input member and the input memberrotates relative to the output member, the cam surface displaces thefollower along a line of action coaxial or parallel with the spring. Theline of action is transverse to the rotational axis and does notintersect the rotational axis.

The present invention provides, in yet another aspect, a rotary powertool comprises a motor, an output shaft, and a clutch mechanismpositioned between the motor and the output shaft to transfer torquefrom the motor to the output shaft. The clutch mechanism includes aninput member to which torque from the motor is transferred and an outputmember co-rotatable with the input member, the output member defining arotational axis. The clutch mechanism further includes a cam surfaceformed on one of the input member or the output member and a compressionspring carried by the other of the input member or the output member forco-rotation therewith. The clutch mechanism also includes a followerhaving a circular cross-sectional shape biased against the cam surfaceby the compression spring. In response to relative rotation between theinput member and the output member, the cam surface displaces thefollower along a line of action coaxial or parallel with the spring. Theline of action does not intersect the rotational axis.

Other features and aspects of the invention will become apparent byconsideration of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a rotary power tool with some portionsomitted.

FIG. 2 is a plan view of the rotary power tool of FIG. 1 with thehousing removed, illustrating a clutch mechanism in accordance with anembodiment of the invention.

FIG. 3 is an exploded perspective view of the clutch mechanism of FIG.2.

FIG. 4 is an assembled cross-sectional view of the clutch mechanism ofFIG. 2.

FIG. 5 is a perspective view of a clutch driver of the clutch mechanismof FIG. 3.

FIG. 6 is a plan view of a clutch gear of the clutch mechanism of FIG.3.

FIG. 7 is an enlarged view of a cam surface on the clutch gear of FIG.6.

FIG. 8 is a front perspective view of the clutch mechanism of FIG. 2.

FIG. 9 is a rear perspective view of the clutch mechanism of FIG. 2.

FIGS. 10-21 are plan views of the clutch mechanism, illustrating asequence of operation.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

With reference to FIG. 1, a rotary power tool 10, such as a core drill,includes a motor 14 and an output shaft 18 that receives torque from themotor 14. A tool bit (not shown) is coupled for co-rotation with theoutput shaft 18 to perform work on a workpiece. With reference to FIG.2, the power tool 10 also includes a clutch mechanism 22 positionedbetween the motor 14 and the output shaft 18 to limit the amount oftorque that can be transmitted from the motor 14 to the output shaft 18,and a transmission 26 positioned between the clutch mechanism 22 and theoutput shaft 18. The power tool 10 may be powered by an on-board powersource (e.g., a battery, not shown) or a remote power source (e.g., analternating current source) via a cord (also not shown).

With reference to FIG. 3, the clutch mechanism 22 includes an inputmember or outer ring 30 having outer teeth 34 meshed with a pinion gear38 (FIG. 2) which, in turn, is attached to an output shaft 42 of themotor 14. Because the outer ring 30 and the pinion gear 38 arecontinuously enmeshed, the outer ring 30 will rotate in response torotation of the motor output shaft 42. The clutch mechanism 22 alsoincludes an output member or clutch driver 46 (FIG. 3) coupled forco-rotation with an intermediate shaft 50 of the transmission 26 (FIG.4). The clutch driver 46 includes a hub 54 defining therethrough acentral aperture 58 in which a portion of the intermediate shaft 50having a corresponding cross-sectional shape is received. In theillustrated embodiment of the clutch mechanism 22 shown in FIG. 3, theaperture 58 has a non-circular “double-D” shape. Alternatively, othernon-circular shapes (e.g., shapes coinciding with splines or a key andkeyway arrangement) may be used. Alternatively, the aperture 58 may havea circular cross-sectional shape in which a portion of the intermediateshaft 50 having a corresponding circular cross-sectional shape isreceived via a heavy press fit. The clutch driver 46 also includes arear end cap 62 integrally formed as a single piece with the hub 54 anda front end cap 66 secured to the hub 54 (e.g., using an interferencefit or another joining method). The outer ring 30 is axially constrainedbetween the end caps 62, 66, such that the only degree of freedombetween the outer ring 30 and the clutch driver 46 is rotation. In analternative embodiment of the clutch mechanism 22, the rear end cap 62may be separately formed from the hub 54 and secured thereto using aninterference fit or another joining method similarly to the front endcap 66.

With reference to FIGS. 3 and 5, the clutch driver 46 includes multiplepockets 70 extending in an axial direction of the hub 54 between the endcaps 62, 66. Each of the pockets 70 is positioned between the centralaperture 58 and a cylindrical outer periphery 74 of the hub 54. Each ofthe pockets 70 includes an opening 78 (FIG. 5) at the circumferentialouter periphery 74 of the hub 54 and an opposite base 82 at which thepocket 70 terminates within the hub 54. As shown in FIG. 5, the base 82of each of the pockets 70 is oriented transverse to a rotational axis 86of the clutch driver 46 through the central aperture 58.

The clutch mechanism 22 further includes at least one compression spring90 within each pocket 70 (FIG. 3). In the illustrated embodiment of theclutch mechanism 22, two adjacent compression springs 90 are carriedwithin each pocket 70. To prevent coil binding, a separator such as athin sheet of metal (not shown) may be provided within the pocket 70between the adjacent springs 90. As shown in FIG. 10, one end of each ofthe springs 90 is abutted against the base 82 of the pocket 70 in whichthe respective springs 90 reside, and an opposite end of each of thesprings 90 protrudes from (or is at least proximate to) the openings 78of the respective pockets 70. When positioned within the pockets 70, therespective longitudinal axes 92 of the springs 90 are orientedtransverse to the rotational axis 86 of the clutch driver 46 (FIG. 4).

With reference to FIG. 3, the clutch mechanism 22 also includes afollower 94 disposed proximate the opening 78 of each pocket 70. Eachfollower 94 is biased outward by corresponding pairs of compressionsprings 90 against an interior surface 98 of the outer ring 30. In theillustrated embodiment of the clutch mechanism 22, the followers 94 havea circular cross-sectional shape as viewed in the axial direction, andare therefore configured as cylindrical rollers. Alternatively, thesingle cylindrical roller 94 for each pair of adjacent compressionsprings 90 may be replaced with dual spherical rollers associated withthe respective springs 90.

Each of the followers 94 includes, on each side, a protruding portion102 of a reduced diameter received within respective slots 106, 110 inthe end caps 62, 66 (FIGS. 8 and 9). As shown in FIG. 5, the slots 106in the rear end cap 62 are associated with the pockets 70 and aregenerally located proximate the openings 78 of the pockets 70. The slots106 define longitudinal axes 116 parallel with the longitudinal axes ofthe springs 90. Like slots 110 are also located in the front end cap 66(FIG. 8) and are oriented in the same direction as the slots 106 in therear end cap 62 to constrain displacement of the followers 94 along thedirection of the slot axes 116. Accordingly, when the followers 94 aredisplaced into the pockets 70 against the bias of the springs 90, suchdisplacement is constrained to be along a line of action 112 (FIG. 10)parallel with the longitudinal axes 92 of the corresponding springs 90with which the followers 94 are in contact. Although not shown, theclutch mechanism 22 is packed with a lubricant (e.g., grease) betweenthe interface of the outer ring 30 and the clutch driver 46.

With reference to FIG. 6, the outer ring 30 includes cam surfaces 114defined on the interior surface 98 of the outer ring 30 associated withthe respective followers 94. In the illustrated embodiment of the clutchmechanism 22, the cam surfaces 114 are defined by recesses, each ofwhich is defined by a composite multi-radius arc (FIG. 7). Adjacent eachside of each of the cam surfaces 114, a segment S1 of the interiorsurface 98 of the outer ring 30 is defined by a minor radius R1 havingan origin at the geometric center 118 of the outer ring 30 (FIG. 6). Forpurposes of illustration only, this geometric center 118 is shown bycrosshairs in FIGS. 6 and 13. Adjacent the segment S1 on the left sideof the cam surface 114 from the frame of reference of FIG. 7 is a firsttransition segment S2 of the cam surface 114, which in turn is adjacenta mating segment S3 with which a respective follower 94 is in contactduring normal operation of the power tool 10 below the predeterminedvalue of torque at which the clutch mechanism 22 slips. Although notseparately identified, a small exit radius is formed between thesegments S1, S2 to eliminate a sharp edge between the segment S1 and thecam surface 114. For purposes of illustration only, the boundaries ofthe segments S1, S2, S3, as well as the remaining segments describedbelow, are shown by tick lines intersecting the cam surface 114 in FIG.7. The mating segment S3 of the cam surface 114 is defined by a radiusR2 that is nominally greater than the radius of the follower 94 itself,whereas the first transition segment S2 is a straight line tangent tothe mating segment S3 that joins the segment S1 to the mating segmentS3. Still viewing FIG. 7, to the right of the mating segment S3 is asegment S4 of the interior surface 98 of the outer ring 30 defined by amajor radius R3 having an origin at the geometric center 118 of theouter ring 30. The major radius R3 is greater than all the other radiidefining the cam surface 114. Still viewing FIG. 7, to the right of thesegment S4 is a connecting segment S5, the radius R4 of which is lessthan the radius R3 of the segment S4 but greater than the radius R2 ofthe mating segment S3. Lastly, to the right of the connecting segment S5is a small entrance radius (not separately labeled) to eliminate a sharpedge between the segment S5 and the segment S1. Each of the cam surfaces114 in the outer ring 30 is identical to the cam surface 114 shown inFIG. 7.

In operation of the power tool 10, an operator actuates a trigger (notshown) on the power tool 10 to drive the motor 14, causing the motorshaft 42 to rotate the outer ring 30 in a clockwise direction from theframe of reference of FIG. 10. Below the predetermined value of torqueat which the clutch mechanism 22 slips, the springs 90 maintain thefollowers 94 abutted against the mating segments S3 of the respectivecam surfaces 114. Therefore, as the outer ring 30 rotates in a clockwisedirection, the mating segments S3 of the respective cam surfaces 114apply a normal force N to the follower 94 and springs 90 along a line ofaction 112 parallel with the longitudinal axes 92 of the springs 90.Because the springs 90 bear against the base 82 of the respectivepockets 70, the normal force N is also applied to the clutch driver 46in a direction transverse to the rotational axis 86 of the clutch driver46, imparting a moment to the clutch driver 46 and causing it toco-rotate with the outer ring 30. And, because the intermediate shaft 50is coupled for co-rotation with the clutch driver 46, torque istransmitted to the intermediate shaft 50, which then drives thetransmission 26 and the output shaft 18 of the power tool 10.

However, when the reaction torque applied to the output shaft 18 of thepower tool 10 approaches the predetermined value at which the clutchmechanism 22 slips, the outer ring 30 begins to rotate relative to theclutch driver 46 (in a clockwise direction, shown in sequence in FIGS.10-21), causing the followers 94 to slide and/or roll along the matingsegments S3 of the respective cam surfaces 114 while being displacedalong the line of action 112. Displacement of the followers 94 isconstrained along the line of action 112 by the shape of the guide slots106, 110 in the rear and front end caps 62, 66. As a result, thefollowers 94 cannot slide and/or roll relative to the pockets 70 in adirection transverse to the line of action 112, eliminating any frictionthat might otherwise develop between the followers 94 and the pockets 70from such movement. Furthermore, the variability of such frictionalforces is also eliminated, reducing the overall variability in thetorque value at which the clutch mechanism 22 slips. While the followers94 are gradually displaced into the pockets 70 and as the springs 90gradually compress in a corresponding manner, the followers 94 graduallyslide and/or roll from the mating segments S3 of the respective camsurfaces 114 toward the first transition segment S2, as shown in FIGS.11 and 12.

Upon the followers 94 reaching the first transition segment S2 (FIG.13), the component of the normal force N imparted on the followers 94 bythe cam surface 114 (resolved along the line of action 112) is at itshighest value. At this time, a radius of contact R5 exists between thegeometric center 118 of the outer ring 30 and a point 122 tangent toeach of the followers 94 and the respective cam surface 114. In otherwords, the radius of contact R5 is the radius of a phantom circle 126that is coaxial with the geometric center 118 of the outer ring 30 andthat intersects the tangent points 122 when the component of the normalforce N applied to the followers 94 by the cam surface 114 (resolvedalong the line of action 112) is at its highest value. In one embodimentof the clutch mechanism 22, the radius of contact R5 is less than about0.9 inches. In another embodiment of the clutch mechanism 22, the radiusof contact R5 is less than about 0.8 inches. In yet another embodimentof the clutch mechanism 22, the radius of contact R5 is between about0.9 inches and about 0.7 inches. In a further embodiment of the clutchmechanism 22, the radius of contact R5 is about 0.7 inches. Bymaintaining a small radius of contact R5, the clutch mechanism 22 canimpart more of the motor's torque to the output shaft 18 of the powertool 10, while fitting within a smaller design envelope.

Upon continued rotation of the outer ring 30 relative to the clutchdriver 46, the followers 94 disengage the cam surfaces 114 (first shownin FIG. 14) and transition into contact with the segments S1, causingthe component of the normal force N resolved along the line of action112, applied to the clutch driver 46 through each of the followers 94,to be quickly reduced to zero or a nominal value insufficient to imparta moment to the clutch driver 46 to cause its continued rotation. Atthis time, the clutch driver 46, the intermediate shaft 50, thetransmission 26, and the output shaft 18 seize. But, continuedactivation of the motor 14 drives the outer ring 30 in a clockwisedirection, causing it to slip relative to the clutch driver 46 as shownin the sequence of FIGS. 14-19.

As shown in FIGS. 17-19, the outer ring 30 continues to rotate about theclutch driver 46 while the followers 94 slide and/or roll along theinterior surface segments S1 until the followers 94 reach the nextadjacent cam surface 114, at which time the compression springs 90rebound and push the followers 94 onto the cam surfaces 114. As shown inFIGS. 20 and 21, the followers 94 slide and/or roll along the connectingsegments S5 and the segments S4 of the respective cam surfaces 114before re-engaging the mating segments S3 of the respective cam surfaces114 (FIG. 10). If the reaction torque on the output shaft 18 of thepower tool 10 continues to remain above the predetermined value at whichthe clutch mechanism 22 slips, the outer ring 30 will continue to rotaterelative to the clutch driver 46 as shown in the sequence of FIGS.11-21. However, if the reaction torque on the output shaft 18 of thepower tool 10 falls below the predetermined value at which the clutchmechanism 22 slips, upon the followers 94 re-engaging the matingsegments S3 of the respective cam surfaces 114, a normal force N isagain applied to the followers 94 to impart a moment to the clutchdriver 46 to cause it to rotate.

In alternative embodiments of the clutch mechanism 22, the springs 90could be set in pockets 70 defined in the outer ring 30 (i.e., the inputmember) and the cam surfaces 114 could be defined on the clutch driver46 (i.e., the output member), with the clutch mechanism 22 functioningin the same manner as described above.

Because the cam surfaces 114 displace the followers 94 along a line ofaction 112 parallel with the longitudinal axes 92 of the springs 90, thevariability in the torque value at which the clutch mechanism 22 slipsis reduced. Further, the torque value at which the clutch mechanism 22slips is more repeatable. In addition, by using dual springs 90 in eachpocket 70, the clutch mechanism 22 has a higher torque-transmittingcapacity compared to conventional clutch mechanisms (which use a singlespring per pocket) for use with rotary power tools. As mentioned above,the clutch mechanism 22 also provides a reduced radius of contact R5compared to conventional clutch mechanisms for use with rotary powertools, which saves on material costs and reduces the size of the tool,which provides greater portability.

Various features of the invention are set forth in the following claims.

What is claimed is:
 1. A clutch mechanism for use in a rotary power toolhaving a motor, the clutch mechanism comprising: an input member towhich torque from the motor is transferred; an output memberco-rotatable with the input member, the output member defining arotational axis; a cam surface formed on one of the input member or theoutput member; a compression spring carried by the other of the inputmember or the output member for co-rotation therewith; and a followerhaving a circular cross-sectional shape biased against the cam surfaceby the compression spring, such that the cam surface applies a normalforce to the follower, wherein in response to the output memberco-rotating with the input member, the normal force applied to thefollower is along a line of action that is coaxial or parallel with thespring and does not intersect the rotational axis, and wherein, inresponse to relative rotation between the input member and the outputmember, the cam surface displaces the follower along the line of action.2. The clutch mechanism of claim 1, wherein the cam surface is a recessdefined on an interior surface of the input member.
 3. The clutchmechanism of claim 2, wherein when the motor transfers torque to theinput member and when the normal force applied to the follower by thecam surface is at a maximum value, a radius of contact exists between ageometric center of the input member and a point tangent to the followerand the cam surface, and wherein the radius of contact is less than 0.9inches and greater than or equal to 0.7 inches.
 4. The clutch mechanismof claim 2, wherein the cam surface is a multi-radius arc recess.
 5. Theclutch mechanism of claim 4, wherein the cam surface includes a matingsegment that is defined by a mating radius that is nominally greaterthan a radius of the follower.
 6. The clutch mechanism of claim 5,wherein when the motor transfers torque to the input member and when thespring biases the follower against the mating segment, the output memberco-rotates with the input member.
 7. The clutch mechanism of claim 5,wherein the cam surface includes a transition segment between theinterior surface and the mating segment, and wherein the transitionsegment is a straight line tangent to the mating segment.
 8. The clutchmechanism of claim 7, wherein when the follower is engaged against thetransition segment, the normal force applied to the follower by the camsurface is at a maximum value.
 9. The clutch mechanism of claim 8,wherein when the motor transfers torque to the input member and thefollower moves from the transition segment to the interior surface, theoutput member stops rotating and the input member continues rotating.10. The clutch mechanism of claim 7, wherein the cam surface includes anouter segment adjacent to the mating segment, the outer segment beingdefined by a major radius having an origin at a geometric center of theinput member, and wherein the cam surface includes a connecting segmentadjacent to the outer segment, the connecting segment defined by aconnecting radius that is less than the major radius and greater thanthe mating radius.
 11. The clutch mechanism of claim 1, wherein thefollower includes a protruding portion with a circular cross-sectionalshape having a diameter that is smaller than a diameter of the circularcross-sectional shape of the follower.
 12. The clutch mechanism of claim11, wherein one of the input member or the output member defines a slotthat defines a longitudinal axis that is parallel to the line of action,and wherein the protruding portion is received within the slot.
 13. Theclutch mechanism of claim 1, wherein the compression spring is one oftwo compression springs, and wherein the follower is biased against thecam surface by each of the two compression springs, and wherein the lineof action is coaxial or parallel with each of the two compressionsprings.
 14. The clutch mechanism of claim 1, wherein the member thatcarries the compression spring defines a pocket in which the compressionspring is received, the pocket being oriented transverse to therotational axis, such that the line of action is transverse to therotational axis.
 15. A clutch mechanism for use in a rotary power toolhaving a motor, the clutch mechanism comprising: an input member towhich torque from the motor is transferred, the input member having aninterior surface and defining a cam surface recessed in the interiorsurface; an output member co-rotatable with the input member, the outputmember carrying a compression spring for co-rotation therewith anddefining a rotational axis; and a follower biased against the camsurface by the compression spring, wherein when the motor transferstorque to the input member and the follower is maintained against thecam surface, the output member co-rotates with the input member, andwherein when the motor transfers torque to the input member and theinput member rotates relative to the output member, the cam surfacedisplaces the follower along a line of action coaxial or parallel withthe spring, and wherein the line of action is transverse to therotational axis and does not intersect the rotational axis.
 16. Theclutch mechanism of claim 15, wherein the output member defines a pocketin which the compression spring is received, and wherein the pocket isoriented transverse to the rotational axis, and coaxial or parallel withthe line of action.
 17. The clutch mechanism of claim 15, wherein whenthe motor transfers torque to the input member and a normal forceapplied to the follower by the cam surface is at a maximum value, aradius of contact exists between a geometric center of the input memberand a point tangent to the follower and the cam surface, and wherein theradius of contact is less than 0.9 inches and greater than or equal to0.7 inches.
 18. A rotary power tool comprising: a motor; an outputshaft; and a clutch mechanism positioned between the motor and theoutput shaft to transfer torque from the motor to the output shaft, theclutch mechanism including an input member to which torque from themotor is transferred, an output member co-rotatable with the inputmember, the output member defining a rotational axis, a cam surfaceformed on one of the input member or the output member, a compressionspring carried by the other of the input member or the output member forco-rotation therewith, the spring defining a longitudinal axis, and afollower having a circular cross-sectional shape biased against the camsurface by the compression spring, such that the cam surface applies anormal force to the follower, wherein in response to the output memberco-rotating with the input member, the normal force applied to thefollower is along a line of action that is coaxial or parallel with thelongitudinal axis and does not intersect the rotational axis, andwherein, in response to relative rotation between the input member andthe output member, the cam surface displaces the follower along the lineof action.
 19. The rotary power tool of claim 18, wherein the camsurface is a recess defined on an interior surface of the input member.20. The rotary power tool of claim 19, wherein when the motor transferstorque to the input member and the normal force applied to the followerby the cam surface is at a maximum value, a radius of contact existsbetween a geometric center of the input member and a point tangent tothe follower and the cam surface, and wherein the radius of contact isless than 0.9 inches and greater than or equal to 0.7 inches.